1. Field of the Invention
The present invention relates to a computer simulation method for a semiconductor device manufacturing process, and more specifically to a method for establishing a region that is changed to an amorphous state.
2. Description of Related Art
There has been an attempt made to optimize a semiconductor device manufacturing process, such as, for example, LSI or the like, by means of a process simulator.
The term process simulator in this sense refers to the calculation, using a computer, of a semiconductor device manufacturing process such as an ion implantation process or diffusion process, and the prediction of physical quantities and shapes of the device's internal impurities profile and the like.
If a process is optimized by using a process simulator so that the semiconductor device exhibits the best electrical characteristics, it is possible to make a great reduction of both cost and required time in comparison with actually fabricating prototypes of semiconductor devices, for example, LSI devices.
Because the internal physical quantities in a semiconductor device are calculated by a process simulator, it is possible to analyze the behavior of impurities within the semiconductor.
A detailed description of a process simulator is presented pages 18 to 79 of "Process Device Simulation Technology" (published by Sangyo Tosho), edited by Dan Ryo, which was published on Apr. 20, 1990.
In a diffusion simulation which is used for the purpose of calculating a diffusion process, it is necessary to solve the diffusion equations for each of the impurities which express the behavior of the impurities within the semiconductor.
It has been reported that point defects in inter-lattice silicon occurring because of ion implantation and at holes and the like can interact with implanted ions so as to accelerate the diffusion of impurities, in the IEEE Transactions on Electron Devices, Vol. 40, No. 7, pages 1215 to 1222, in H. Hane and H. Matsumoto "A Model for Boron Short Time Annealing After Ion Implantation" published July 1993, and to calculate this type of phenomenon using a computer, it is necessary also to simultaneously solve the diffusion equation for point defects in inter-lattice silicon and holes or the like occurring because of ion implantation.
In a region in which ion implantation causes a large number of point defects, because of a collapse of the crystalline structure, there is a change to an amorphous state.
In a region that has changed to an amorphous state, because the initial conditions of impurities and point defects and the like are different from the crystalline region, to achieve an accurate simulation of the impurity diffusion, it is necessary to accurately establish the region in which the change to an amorphous state has occurred.
In the past, as noted in H. Cerva and G. Hobler, "Comparison of Transmission Electron Microscope Cross Sections of Amorphous Regions in Ion Implanted Silicon with Point-Defect Density Calculations" (Journal of Electrochemical Society, Vol. 139, No. 12, p. 3631-3638, December, 1992), a method of establishing a region that has become amorphous by using the point-defect density that occurs due to ion implantation was used.
In this method, as shown in FIG. 3, the region in which the point-defect density 21 that occurs because of ion implantation is at or above some density D.alpha. is taken as the region that has become amorphous.
Using the prior art, it is difficult to improve the accuracy of establishing the region that has become amorphous.
The reason for this is that the point-defect density occurring because of ion implantation is used to establish the region that has become amorphous.
Since the actual measurement of the point-defect density is difficult, it is difficult to know its precise value, this making it necessary to determine it by means of ion implantation simulation, which not only is highly dependent upon the ion implantation simulator model and parameters, but also because these models include approximations it is difficult to obtain parameters to accurately establish the region that has become amorphous.
In view of the above-described drawbacks in the prior art, an object of the present invention is to provide a method of establishing the region that has become amorphous which is capable of determining this region accurately.